The industrial production of complex biopharmaceuticals using recombinant mammalian cell lines is still mainly built on a quality by testing approach, which is represented by fixed process conditions and extensive testing of the end-product. In 2004 the FDA launched the process analytical technology initiative, aiming to guide the industry towards advanced process monitoring and better understanding of how critical process parameters affect the critical quality attributes. Implementation of process analytical technology into the bio-production process enables moving from the quality by testing to a more flexible quality by design approach. The application of advanced sensor systems in combination with mathematical modelling techniques offers enhanced process understanding, allows on-line prediction of critical quality attributes and subsequently real-time product quality control. In this review opportunities and unsolved issues on the road to a successful quality by design and dynamic control implementation are discussed. A major focus is directed on the preconditions for the application of model predictive control for mammalian cell culture bioprocesses. Design of experiments providing information about the process dynamics upon parameter change, dynamic process models, on-line process state predictions and powerful software environments seem to be a prerequisite for quality by control realization. Keywords: Biopharmaceutical production · Design of experiments · Mathematical modelling · Process analytical technology · Soft-sensingCorrespondence: Dr. Gerald Striedner, Department of Biotechnology (DBT), University of Natural Resources and Life Sciences (BOKU), Muthgasse 18, 1190 Vienna, Austria E-mail: gerald.striedner@boku.ac.at Abbreviations: CHO, Chinese hamster ovary; CPP, critical process parameter; CQA, critical quality attribute; DCS, distributed control system; DoE, design of experiments; FDA, Food and Drug Administration; iDoE, intensified design of experiments; MBDoE, model based design of experiments; MPC, model predictive control; MVDA, multivariate data analysis; PAT, process analytical technology; QbD, quality by design; SCADA, supervisory control and data acquisition; TPP, target product profile

Broadly neutralizing anti-HIV-1 monoclonal antibodies, such as PG9, and its derivative RSH hold great promise in AIDS therapy and prevention. An important feature related to the exceptional efficacy of PG9 and RSH is the presence of sulfated tyrosine residues in their antigen-binding regions. To maximize antibody functionalities, we have now produced glycan-optimized, fucose-free versions of PG9 and RSH in Nicotiana benthamiana. Both antibodies were efficiently sulfated in planta on coexpression of an engineered human tyrosylprotein sulfotransferase, resulting in antigen-binding and virus neutralization activities equivalent to PG9 synthesized by mammalian cells ( CHO PG9). Based on the controlled production of both sulfated and nonsulfated variants in plants, we could unequivocally prove that tyrosine sulfation is critical for the potency of PG9 and RSH. Moreover, the fucose-free antibodies generated in N. benthamiana are capable of inducing antibody-dependent cellular cytotoxicity, an activity not observed for CHO PG9. Thus, tailoring of the antigen-binding site combined with glycan modulation and sulfoengineering yielded plant-produced anti-HIV-1 antibodies with effector functions superior to PG9 made in CHO cells.onoclonal antibodies (mAbs) offer great promise for AIDS treatment (1). In particular, the recent discovery of broadly neutralizing anti-HIV-1 mAbs (bNAbs) with extraordinary potency as exemplified by the antibodies PG9, PG16 (2), or those of the PGT series (3) creates hope for effective therapy by passive antibody transfer. PG9 and its close relative PG16 neutralize ∼80% of HIV-1 isolates across all clades (2, 4). The recognized epitopes are within the hypervariable and heavily glycosylated V1/V2 loops of the viral envelope glycoprotein gp120 and preferentially displayed in its trimeric state (2). Both mAbs use their unusually long complementarity-determining region (CDR) H3 domains (4-6) to penetrate the glycan shield of the virus and make contact with the underlying protein backbone (7). In addition, PG9 and PG16 recognize two highly conserved gp120 N-glycans attached to Asn 160 and Asn 156/173 , which flank the peptide epitope (7-9). Remarkably, the glycan-binding properties of the two antibodies could be combined by modification of the PG9 light chain with R L94

Upon stable cell line generation, chromosomal integration site of the vector DNA has a major impact on transgene expression. Here we apply an active gene environment, rather than specified genetic elements, in expression vectors used for random integration. We generated a set of Bacterial Artificial Chromosome (BAC) vectors with different open chromatin regions, promoters and gene regulatory elements and tested their impact on recombinant protein expression in CHO cells. We identified the Rosa26 BAC as the most efficient vector backbone showing a nine-fold increase in both polyclonal and clonal production of the human IgG-Fc. Clonal protein production was directly proportional to integrated vector copy numbers and remained stable during 10 weeks without selection pressure. Finally, we demonstrated the advantages of BAC-based vectors by producing two additional proteins, HIV-1 glycoprotein CN54gp140 and HIV-1 neutralizing PG9 antibody, in bioreactors and shake flasks reaching a production yield of 1 g/l.

Chinese hamster ovary (CHO) cells are the most commonly used mammalian hosts for the production of biopharmaceuticals. To overcome unfavorable features of CHO cells, a lot of effort is put into cell engineering to improve phenotype. “Omics” studies investigating elevated growth rate and specific productivities as well as extracellular stimulus have already revealed many interesting engineering targets. However, it remains largely unknown how physicochemical properties of the recombinant product itself influence the host cell. In this study, we used quantitative label‐free LC‐MS proteomic analyses to investigate product‐specific proteome differences in CHO cells producing two similar antibody fragments. We established recombinant CHO cells producing the two antibodies, 3D6 and 2F5, both as single‐chain Fv‐Fc homodimeric antibody fragments (scFv‐Fc). We applied three different vector strategies for transgene delivery (i.e., plasmid, bacterial artificial chromosome, recombinase‐mediated cassette exchange), selected two best performing clones from transgene variants and transgene delivery methods and investigated three consecutively passaged cell samples by label‐free proteomic analysis. LC‐MS‐MS profiles were compared in several sample combinations to gain insights into different aspects of proteomic changes caused by overexpression of two different heterologous proteins. This study suggests that not only the levels of specific product secretion but the product itself has a large impact on the proteome of the cell. Biotechnol. Bioeng. 2016;113: 1902–1912. © 2016 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.